A plastic binder for binding sheets of loose-leaf paper and documents perforated with multiple-hole paper punchers (refer to JP-A-2000-289376, for example) are known. A binder of the sort mentioned above will be described briefly herein below. FIGS. 20, 21 and 22 show a conventional binder 1 with a number of ½ ring parts 3 and 4 arranged at constant intervals on both side edges of spine portions 2, which are respectively formed into double-split hinges by monolithic molding. As shown in the drawings above, a projection 5 is formed at the tip of each ½ ring part 3 in the upper line and has a bulged tip, whereas a depression 6 corresponding in configuration to the bulged tip of the projection 5 is formed in the tip of each ½ ring part 4 in the lower line so that the upper and lower ½ ring parts 3 and 4 can be engaged together by press-fitting the projection 5 into the depression 6. When sheets of loose-leaf paper are bound with the binder 1, the ½ ring parts 3 lined up on one side or the ½ ring parts 4 lined up on the other are passed through the holes of the paper and the two lines of ½ ring parts 3 and 4 are closed up manually. As the projections 5 of the ½ ring parts 3 are engaged with the depressions 6 of the ½ ring parts 4 to form rings, the sheets of loose-leaf paper are bound up.
Heretofore, the work of binding documents with a binder has been done manually and it takes much labor to follow the steps of passing many ½ ring parts through the holes of paper and closing the two lines of ½ ring parts manually. Moreover, this work requires a great deal of time, particularly when many documents are bound up. It is therefore an object of the invention to provide a binding apparatus capable of efficiently doing binding work by means of a plastic binder without using the hands.
When a binding apparatus for performing a binding process is constructed, it will become necessary to provide a holding mechanism for setting a binder to face the back of loose-leaf paper by clutching the spine portion of the binder and an engaging mechanism for engaging the ½ ring parts of the binder by closing the ½ ring parts. Since the spine portion of the conventional binder is in the form of a double-split hinge and opened and closed together with the ½ ring parts, the holding mechanism is hardly able to keep hold of the spine portions when the engaging mechanism closes the ½ ring parts. Consequently, there is the possibility that the binder will slip off the holding mechanism, so that the conventional binder is considered unfeasible for use in the binding apparatus. It is therefore another object of the invention to provide a binder adapted for being usable by a binding apparatus.
Further, the above conventional binder is in the form of a double-split ring and when the plurality of binders are stacked up, there is produced a gap between the binders as shown in FIG. 21(b) because of the difference between the inner and the outer diameters of the respective ½ ring parts 3 and 4. The drawback is that it is inconvenient to carry the binders as the binders may be dismembered while being handled and the binders are rendered bulky when they are packaged. In case that the binding process is mechanized, moreover, a large amount of binders are necessarily charged into a binding machine and the conventional binder will necessitate a large storage space and this constitutes an obstacle to reducing the machine size. It is therefore still another object of the invention to provide a space-saving, easy-to-handle binder.
In the case of the above conventional binder, further, the projection projected circumferentially from the tip of each ½ ring part on one side and the depression formed in the tip of each ½ ring part on the other are used for forming the engaging means for engaging the ½ ring parts. Therefore, use has to be made of a pattern drawing means such as rotary drawing for forming the projection in such a shape that its tip is bulged and the depression 6 in such a shape that its interior is also bulged symmetrically about the projection, so that the metal mold tends to become complicated in structure, thus increasing the production cost. Although the number of sheets that can be bound up is increased by decreasing the thickness of the ring part in its radial direction, the projection and the depression will have to be made to the suitable measurements so as to secure the engaging strength, which causes the tip portion of the ring part to necessarily grow thicker than the diameters of the projection and the depression, whereby it is difficult to form a slender ring part. It is therefore a further object to decrease the production cost of a binder as well as forming slender ring parts.